Separator plate and electrochemical system

ABSTRACT

A separator plate for an electrochemical system has two metal individual plates. The plates have passage openings for operating media and possibly coolant, and distribution structures. The distribution structures are formed in the metal individual plates and which each communicate with at least two of the passage openings. A peripherally extending sealing structure is formed in each of the metal individual plates at least peripherally around the electrochemically active region and at a distance therefrom and/or peripherally around at least one of the passage openings and at a distance from the edge thereof. The cross-section of the sealing structure has a bead roof, two bead flanks, and at least in some segments, two bead feet. At least in the region of the bead roof of the sealing structure at least in some segments, the sealing structure extends sinuously with at least two wave periods having convex and concave segments.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 15/519,974, entitled “SEPARATOR PLATE WITH DECREASED WIDTH OF ONEBEAD FLANK AND ELECTROCHEMICAL SYSTEM”, and filed on Apr. 18, 2017. U.S.patent application Ser. No. 15/519,974 is a U.S. national phase ofInternational Application No. PCT/EP2015/074016, entitled “SEPARATORPLATE AND ELECTROCHEMICAL SYSTEM”, and filed on Oct. 16, 2015.International Application No. PCT/EP2015/074016 claims priority toGerman Utility Model Application No. 20 2014 008 375.4, entitled“SEPARATOR PLATE AND ELECTROCHEMICAL SYSTEM”, and filed on Oct. 18,2014. The entire contents of each of the above-listed applications arehereby incorporated by reference for all purposes.

TECHNICAL FIELD

The invention relates to a separator plate for an electrochemicalsystem, as well as to such an electrochemical system.

BACKGROUND

The separator plate can be used for example for a fuel cell system inwhich electrical energy is obtained from hydrogen and oxygen. Theseparator plate can also be used for an electrolyser in which hydrogenand oxygen are produced from water by way of applying a potential. Theseparator plate can likewise be used for an electrochemical compressorin which molecular hydrogen is transported through the membrane due tooxidation/reduction by way of applying a potential, and issimultaneously compressed. Moreover, the separator plate can also beused for a humidifier for an electrochemical system in which a dry gasto be fed to an electrochemical system is humidified by way of a humidgas, mostly an exhaust gas of an electrochemical system.

Usually, separator plates for an electrochemical system comprise a platepair with two metallic individual plates, wherein in each case twoseparator plates surround an electrochemical cell, for example a fuelcell, and delimit this from the next electrochemical cell. Herein, in anelectrochemical system a multitude of electrochemical cells, for exampleup to 200, are mostly stacked in series into a stack, in a manner suchthat the cells are then each separated from one another by a separatorplate. The cells themselves usually consist of a membrane electrodeassembly/unit, also called MEA (membrane electrode assembly), as well asin each case of a gas diffusion layer (GDL) which e.g. consists of anelectrically conductive carbon non-woven, on both sides of the MEA. Thecomplete stack is held together between two end plates via a clampingsystem and is provided with q predefined pressing. In the case of ahumidifier, the cell consists of only a membrane, potentially with asupport medium, as well as with porous structures which can be comparedto the GDLs, but which do not need to be electrically conductive.

In an electrochemical system, apart from separation of theelectrochemical cells from one another, the separator plates servefurther functions; these on the one hand being the electrical contactingof the electrodes of the different electrochemical cells, as well as theleading of the current to the respective adjacent cell, and on the otherhand the supplying of the cells with operating media and the removal ofthe reaction products, furthermore the cooling of the electrochemicalcells and the onward transport of the waste heat, as well as the sealingof the compartments of the two different operating media and of thecoolant, to one another as well as to the outside.

Through-openings for operating media, usually on the one hand forhydrogen or methanol in particular and on the other hand for air oroxygen in particular, as well as for coolant, mostly mixtures ofdemineralised water and antifreeze, are accordingly formed in bothmetallic individual plates of the separator plate, for the supply of theelectrochemical cells. Operating media and coolant are hereinaftertogether referred to as media. Moreover, a distribution structure isformed in each of the two metallic individual plates, wherein channelsform on both surfaces of the two individual plates. An operating mediumis conducted on each of the outwardly facing surfaces of the separatorplate, and the coolant is conducted in the intermediate space betweenthe two metallic individual plates. The region in which an operatingmedium is led in a channel structure is also referred to as theelectrochemically active region of the separator plate. Each of thedistribution structures communicates with at least two of thethrough-openings, specifically at least one inlet and at least oneoutlet for the respective fluid. Each of the individual metallic plates,at least in a peripherally closed manner around the electrochemicallyactive region of the separation plate as well as around thethrough-openings, is surrounded by a sealing structure, which isdistanced from the electrochemically active region, or the respectiveedge of the through-opening, so as to seal the different media regionsto one another and to the outside. The sealing of the electrochemicallyactive region can herein be effected such that through-openings whichare sealed with respect to the compartment containing theelectrochemically active region by way of their own peripheral sealingstructures, are arranged within the sealing structure which isperipherally closed around this region.

It has already been suggested in DE 101 58772 A1 to emboss the sealingstructure into the metallic individual plates of the separatorstructure, specifically in the form of a full bead or half beadextending in a straight line. A sealing result satisfying theexpectations at the time could be achieved by these straight-lined beadsin the case of small separator plates having an essentially square basesurface and a small to medium plate number, with a simultaneously highclamping of the stack. However, with beads extending in a straight linein separator plates having rather elongate plate base surfaces, or inlarger separator plates, the sealing result was already mostlyunsatisfactory. With long bead sections running in a straight line, thebeads lose their stiffness with an increasing distance to the cornerpoints and do not have an adequate restoring force in the regionsconcerned.

In WO 2004/036677 A2, an attempt to counter this was made by way of thesealing elements being designed as full beads with a non-linear courseat least in sections. These on the one hand are beads which becomethicker and thinner at both sides in a periodically alternating manner,as well as on the other hand beads which have an overall wave-likecourse in sections. Herein, the base widths of the bead flanks—measuredat right angles to the respective neutral line of the wave-likebead—remain the same over the course of the flanks in the wave-likesections. Consequently, different inner and outer radii, which havedifferent stiffnesses and resiliences form, particularly in the regionof the wave peaks and wave troughs, i.e. the apexes. In each case,alternating homogeneities of the pressing in the contact region of thebead roof which, with respect to bead flanks lying opposite one another,change in a manner opposed to one another, result along both bead flankson account of this. Here, the risk exists of media flowing through thesealing structure in regions of lower bead stiffness, which is to say ofoperating media flowing into the interior of the separator plate and ofcoolant flowing into the outer space of the separator plate. On the onehand, the respective media are lost for the operation of theelectrochemical system. This is not acceptable with regard to theefficiency of the electrochemical system. On the other hand, the riskexists of coolant getting into the region of the operating media and forexample damaging the membrane there.

Due to the large number of separator plates in a stack, a smalldifference in the stiffness and resilience of the sealing bead along itscourse in a single separator plate or in a single metallic individualplate of a separator plate leads to a very large difference in theresiliency of the sealing beads connected/arranged in series, so thatsmall differences at the individual separator plates have a significanteffect on the sealed ness of the complete stack.

SUMMARY

It is therefore the object of the invention to specify a separator platewhich permits a uniform sealing of an electrochemical cell, withoutsignificantly more construction space than is necessary for sealingarrangements of the state of the art being required for the sealing. Thecosts for the separator plate should remain comparable to the costs of aseparator plate of the state of the art, so that the costs of themanufacturing method as well as the material expense should only beincreased insignificantly at the most. The sealing should be able to beapplied for sealing systems without branching and continuations as wellas for those with branching and/or continuations.

This object is achieved by a separator plate according to claims 1 and18 as well as by an electrochemical system according to claim 22.Further developments can be gleaned from the dependent claims.

Thus, the invention relates, one the one hand, to a separator plate foran electrochemical system with two metallic individual plates. Themetallic individual plates each comprise through-openings for operatingmedia and, as the case may be, for coolant, as well as distributionstructures which are formed into the metallic individual plates andwhich each communicate with at least two of the through-openings. Aperipheral sealing structure is formed into each of the metallicindividual plates, at least peripherally around the electrochemicallyactive region and distanced from this and/or peripherally around atleast one of the through-openings and distanced from the edge of thesethrough-openings, the cross section of said sealing structure comprisinga bead roof, two bead flanks and, at least in sections, two bead feet.Herein, delimitation lines form on the bead roof at both sides, whereinthese lines delimit the bead roof running parallel to the plate plane,to the bead flanks inclined to this plane, including a mostly presenttransition radius. Herein, what is essential is that the sealingstructure at least in the region of its bead roof and at least insections runs in a wave-like manner with at least two wave periods withconvex and concave sections, so that upper inner and outer radii form atthe transition from the bead roof to the bead flanks and lower inner andouter radii form at the bead feet. What is different to the state of theart is the fact that although the width (W_(D)) of the bead roof isconstant in the region of its wave-like extension, the base width(W_(I), W_(A)) of at least one of the two bead flanks however changes.By way of this, it is ensured that the complete sealing structure notonly has a uniform sealing behaviour in its potentially present linearregions, but also has a uniform sealing behaviour/uniform stiffness inthe region of the wave-like course of the bead roof at least along atransition from the bead roof to the respective bead flank.

The convex and the concave sections of the wave-like course merge intoone another in each case at an inflection point. A main extensiondirection is superimposed on the wave shape of the bead roof. This mainextension direction results from the connection line of the inflectionpoints of the neutral lines of the bead roof. A convex section thusreaches from one inflection point which is to say from a perpendicularto the tangent to the neutral lines of the bead roof at its inflectionpoint, over an apex projecting to a greater extent from the mainextension direction of the bead, to the next inflection point, and aconvex section reaches from an inflection point which is to say from aperpendicular to the tangent to the neutral lines of the bead roof atits inflection point, over an apex projecting to a lesser extent fromthe main extension direction of the bead, to the next inflection point.For the complete sealing structure, reference is always made to therespective perpendicular to the tangent at the respective point of theneutral lines.

The amplitudes of the delimitation lines of the bead roof can differfrom the amplitudes of the lines of the course of the bead feet, whereasthe wavelengths are identical.

The above also applies to the advantageous embodiment in which at leastone of the bead flanks comprises continuations in the region of thewave-like course of the bead roof, said continuations comprising a roof,two flanks and two feet, wherein these continuations are designed suchthat the total height of the continuations is smaller than the totalheight of the sealing structure, so that the continuations do not affector compromise the actual sealing line, or only to a small extent. Thesecontinuations on the one hand can serve for permitting a passage of amedium transverse to a sealing line. The continuations are preferablyprovided on both sealing flanks for this purpose. However, it is alsopossible to provide continuations at one side, and these form, on thesurface of the individual plate beyond which surface the bead roofprojects, a barrier between a distribution structure and the sealingstructure in order to thus optimally guide the flow of operating mediumor coolant. It is preferable for at least one of these continuations toconnect the interior of the sealing structure to one of the distributionstructures or to one of the through-openings for operating media orcoolant, irrespective of whether a continuation serves for a passage ofa medium or as a barrier. Apart from this, continuations can also serveexclusively as support structures or stiffening structures, and theyherein mostly only have a length which is smaller than fivefold thewidth of the bead roof.

The arrangement of the continuations is herein advantageously effectedsuch that the distance of at least two continuations to one another,preferably all continuations to one another, at a bead flank is n×λ/2,wherein λ is the period length of the wave shape of the bead roof and nis a natural number. The continuations thus for example can be presenton each wave trough and/or each wave peak, of the section of the sealingstructure in which the bead roof has a wave-like course. However, theycan also be arranged at the inflection points of the wave structure. Thenumber of continuations is directed to the respective applicationpurpose and the total length, i.e. the number of wave periods of thewave-like region of the bead roof.

For a uniform sealing, it is advantageous if the base width (W_(I),W_(A)) of at least one of the bead flanks continuously changes, sinceabrupt changes would counteract a uniform sealing.

It is also advantageous for uniform sealing if additionally to thealready described change of the base width of at least one bead flank,the sealing system 10 of the separator plate also has changes of theflank angle in the region of the wave-like extension of the bead roof.Here, the flank angle (α₁) between the bead roof and a bead flankextending in a concave section, and the flank angle (α_(A)) between thebead roof and the opposite bead flank extending in a convex section,change along the wave-like extension region to a different extent, atleast in sections.

Moreover, with regard to the manufacture of the separator plate, it isparticularly advantageous if the lower outer radius in a cross sectionthrough the sealing structure is the same or larger than the upper outerradius. The cross section of the bead in the context of this inventionis always defined perpendicularly to the neutral lines of the bead roof.

Particularly with regard to a uniform sealing of a plate stackcomprising many separator plates, it is particularly advantageous if thebead roofs of the sealing structures of the two metallic individualplates of the separator plate have a mirror-symmetrical course to oneanother with respect to their contact surface. A precise propagation ofthe sealing lines through the complete plate stack is thus achievedgiven a sufficient width of the bead roof, even with slight inaccuraciesof the placing of individual separator plates in the plate stack. Themirror symmetry first and foremost relates to the course of the beadroofs of the sealing structures, but it can also relate to the completesealing structures, wherein it is the potentially present sealingstructures without continuations which are meant here. The height of thesealing structures can moreover also be essentially identical in bothmetallic individual plates of the separator plate. A particularlyuniform pressing and sealing is achieved by way of this, due to the factthat the spring force of the beads is identical in both individualplates.

The sealing structure of the separator plate preferably not only runswith a wave-like bead roof in a single, continuous section, but incontrast, for an optimal sealing, it is advantageous if several sectionsof the bead roof which are connected over the course of the bead but arespatially separated (i.e. e.g. arranged at another location of theplate) each extend in a wave-like manner. Generally, it is possible forthe different sections of the wave-like extension to have differentwavelengths and/or amplitudes, but it is preferable if at least all roofsections of a continuous bead, preferably even all beads which have awave-like course of the bead roof, have the same wavelengths andamplitudes.

Here, on the one hand it is advantageous if, given a peripheral sealingstructure in which several sections of the bead roof extend peripherallyin a closed manner around the electrochemically active region in awave-like manner with at least two wave periods, at least two wave-likesections extend along sides of the electrochemically active region ofthe individual plate, said sides lying opposite one another. Thewave-like sections can also extend in sections along all sides of theelectrochemically active region.

On the other hand, it can be advantageous if, given a peripheral sealingstructure in which several sections of the bead roof extend in awave-like manner with at least two wave periods along an inner edge,that is to say the edge of at least one through—opening for operatingmedia or coolant, of a metallic individual plate, at least two wave-likesections extend along inner edges of the through-opening which lieopposite one another. Here too, it is basically possible for beads witha wave-like bead roof to run sectionally on all inner edges.

Basically, it is advantageous if the wave-like sections of the bead roofextend in those sections of the sealing structure in which the sealingstructure, considered macroscopically, i.e. with regard to its mainextension direction, has a straight-lined course or a weakly arcuatecourse with a radius >15 mm.

The width of the bead roof at least in a section of the wave-like courseof the bead roof is between 0.2 and 2 mm, preferably between 0.9 and 1.2mm. Generally, the width of the bead roof likewise lies in the mentionedregions in the further linear or arcuate course.

The bead sections with the wave-like course of the bead roof, apart froma change of the base width of at least one bead flank, also have achange of the flank angle of the respective bead flank(s). If oneconsiders a convex section of the bead roof, then the adjacent flankangle, beginning at a cross section perpendicular to the tangent throughthe inflection point of the neutral lines, increases up to a crosssection perpendicular to the tangent through the apex of the convexsection of the neutral lines of the bead roof and then decreases againup to the cross section perpendicular to the tangent through the nextinflection point of the neutral lines. Accordingly, the flank angle of aconcave section, beginning at a cross section perpendicular to thetangent through the inflection point of the natural lines, firstlyincreases up to a cross section perpendicular to the tangent through theapex of the concave section of the neutral lines of the bead roof, thusof the minimum, and then increases again up to the cross sectionperpendicular to the tangent through the next inflection point of theneutral lines.

Advantageously, the changes run in a continuous manner. Basically, it isadvantageous if the flank angle of a concave section is smaller than theflank angle of a convex section. The flank angle of a concave sectiongenerally lies between 15° and 60°, preferably between 25° and 50°,whereas the flank angle of a convex section generally lies between 20°and 65°, preferably between 30° and 30 55°. The regions are hereindefined in each case including or excluding the mentioned limits. Onaccount of this, the solution according to the invention differssignificantly from the state of the art, where the flank angle remainsunchanged over the course of the bead.

The change of the flank angle in a concave section between theinflection point and the apex point herein corresponds to a reduction ofup to 50%, preferably of up to 40% with respect to the value at theinflection point, and the change of the flank angle in a convex sectionbetween thee inflection point and the apex point corresponds to anincrease by up to 120%, preferably up to 100%, particularly preferablyby up to 70%, with respect to the value at the inflection point.

The base width of the bead along one of its sections, in which the beadroof runs in a wave-like manner, can only change at one bead flank, butin one embodiment can change at both bead flanks. If it changes at onlyone bead flank, then the change at this flank, if the change is effectedin a convex section, that is in the case of a reduction, is at least 5%,preferably at least 25% with respect to the base width at a crosssection perpendicular to the tangent on one of the adjacent inflectionpoints, and if it is effected at in a concave section, that is in thecase of an increase, the change is at least 5%, preferably at least 20%with respect to the basis width at a cross section perpendicular to atangent on one of the adjacent inflection points. If the base width ofboth bead flanks changes, then the change is between 5 and 70%,preferably between 30 and 55%, with respect to the base width at a crosssection perpendicular to the tangent on one of the adjacent inflectionpoints.

In an advantageous embodiment of the separator plate according to theinvention, the total width of the sealing structure from bead foot tobead foot is constant in the region of a wave-like extension of the beadroof, so that the base widths of the two bead flanks therefore alwayschange in a complementary manner. In a particularly advantageousembodiment, the sealing structure as a whole runs linearly in the regionof the wave-like extension of the bead roof. Here, the spatial equipmentfor the sealing structure is particularly modest.

The invention on the other hand relates to a separator plate for anelectrochemical system comprising two metallic individual plates whicheach comprise through-openings for operating media and, as the case maybe, coolant, as well as distribution structures which are formed intothe metallic individual plates and which each communicate with at leasttwo of the through-openings. Herein, a peripheral sealing structure isformed into each of the metallic individual plates, at leastperipherally around the electrochemically active region and distancedfrom this and/or peripherally around at least one of thethrough-openings and distanced from its edge, the cross section of saidsealing structure comprising a bead roof, two bead flanks and at leastin sections two bead feet. Here too, the sealing structure at least inthe region of its bead roof at least in sections extends in a wave-likemanner with at least two wave periods with convex and concave sections.Here too, upper inner and outer radii form at the transition from thebead roof to the bead flanks, and lower inner and outer radii at thebead feet. This embodiment of the invention is characterised in that atleast at one side adjacent to the bead feet, at least along the regionin which the bead roof extends in a wave-like manner, weld connectionsare sectionally provided between the two metallic individual plates ofthe separator plate, wherein the weld connections in each case extend inthe region adjacent to a convex region of the wave course and preferablyessentially concentrically to the lower outer radius. The distance tothe bead foot herein preferably corresponds to maximally double, inparticular maximally to single the width of the bead roof. Here, theflat sections adjacent to the bead foot which, which without furthermeasures tend to diverge on account of the low spring stiffness, areconnected to one another and the complete separator plate thus obtainsmore structural rigidity. On the other hand, the welding is effected inprecisely the regions in which the structural rigidity is to beincreased, whereas the regions of sufficient structural rigidity orstiffness along the bead feet remain free of weld connections.

In this embodiment of the invention too, one of the bead flanks, in theregion of the wave-like course of the bead roof, can comprisecontinuations having a roof, two flanks and two feet, wherein thesecontinuations are designed such that the total height of thecontinuations is smaller than the total height of the sealing structure.What has been specified before with respect to the continuations applieshere to the same extent.

As already specified, the weld connections only extend in sections.Here, it is preferable if their extension in each case is at least 1/9of the wavelength of the wave-like course of the bead roof. Furthermore,it is preferable if the extension of the weld connection extendsmaximally over the entire convex region of the wave course, thus betweenthe perpendiculars through the inflection points of the neutral lines ofthe bead roof, said inflection points being adjacent one another.

In all embodiments of the invention, it is advantageous if the sealingstructure of an individual plate has a constant height, and it is onlythe potentially present continuations which are excluded. It isparticularly preferable if all individual plates comprise sealingstructures with a constant height.

It is advantageous for all aforesaid embodiments of the separator plateaccording to the invention if the sealing structure comprises a coatingfor microsealing, at least in the region of the bead roof. The coatingherein is deposited for example on at least one, preferably however onboth individual plates, on the bead roof in a manner such that it islocated on the outer side of the separator plate. The coating herein asa binder advantageously comprises FPM (fluorocarbon rubber), siliconerubber or NBR rubber (nitrile butadiene rubber), PUR (polyurethane), NR(natural rubber), FFKM (perfluoroelastomeric compounds), SBR (styrenebutadiene rubber), BR (butyl rubber), FVSQ (fluorosilicone), CSM(chlorosulphonated polyethylene), silicon resin and/or epoxy resin ormixtures of the mentioned substances. The coating can also be a contactadhesive or a physically setting adhesive. This for example can be apermanently sticky adhesive which preferably consists of mixtures ofrubbers and adhesive resins, so called tackifiers, or of a poorly curedrubber, where synthetic and natural resins may be considered as adhesiveresins. Herein, natural and synthetic rubbers, polyacrylates, polyester,polychloroprenes, polyvinylether and/or polyurethanes and/orflouropolymer rubbers can be used as base polymers, to which resins suchas in particular modified natural resins, for example rosin and/orartificial resins—for example polyester resins, phenol resins—as well assofteners and/or antioxidants can be added. Typically, coatingthicknesses for all aforesaid substances are between 5 and 200micrometers.

The metallic layers of the separator plates preferably consist of steel,in particular of stainless steel, wherein conductive coatings can bepresent in the electrochemically active region. In alternativeembodiments, aluminium, titanium, roller-coated, low-alloyed steelswhich are coated e.g. with chromium, stainless steel, niobium, tantalumor chromium-nickel alloys can be used as materials. Common sheet metalthicknesses lie between 50 and 200 micrometers, preferably between 60and 150 micrometers.

Generally, with regard to the separator plates, one can differentiatebetween the bipolar plates, where different media are led on bothsurfaces, and monopolar plates, where the same medium is led on bothsurfaces of a monopolar plate. Here, slightly different monopolar platesare mostly used for both different media. The differences in particularmay relate to the presence of continuations on the sealing beads. Thecourse of the sealing structures and thus their sectionally wave-likedesign in contrast is mostly identical or mirror symmetrical in allplates. The embodiments of this description apply to both plate types,unless the differences are emphasised by explicit mention. Preferably,coolant is led in the intermediate space of the two individual plates ofthe respective plate, and this is the case with both plate types.

The separator plates according to the invention are advantageously usedin an electrochemical system. Such an electrochemical system comprisestwo end plates, as well as a multitude of electrochemical cells whichare separated from one another in each case by a separator plateaccording to the invention. The complete system is herein preferablyheld together by way of clamping means, for example bolts or straps andherein provided with a clamping force which is optimal for sealing.Transition plates whose design differs from the design of the separatorplates of the stack can be provided between the end plates and theoutermost cells of the stack. Mostly, one such transition plate, whichcan also be designed in a multi-layered manner, is present per endplate.

With regard to the electrochemical system, this is preferably a fuelcell system, an electrolyser, an electrochemical compressor system or ahumidifier system for a fuel cell system.

The invention is hereinafter explained in more detail by way of thedrawings. These drawings serve exclusively for explaining preferredembodiment examples of the invention, without the invention beinglimited to this. In the drawings, the same parts are provided with thesame reference numerals. The examples all relate to a fuel cell system,but the explanations also apply to the same extent to the other types ofelectrochemical systems which are mentioned above. Apart from theessential features of the present invention which are specified in theindependent claims, the figures also contain optional furtherdevelopments which would also be advantageous in a differentcomposition. Each individual one of these advantageous and/or optionalfurther developments of the invention as such can be formed into afurther development of the invention specified in the independentclaims, even without combining it with one, several or all of theoptional and/or advantageous further developments which are alsorepresented in the examples.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures schematically show:

FIG. 1 is a schematic representation of an electrochemical system;

FIG. 2a is an exploded representation of an electrochemical cell withtwo separator plates which are adjacent thereto;

FIG. 2b is a partial cross-section of the electrochemical cell and aseparator plate both of FIG. 2 a;

FIG. 2c is a plan view of a separator plate of FIG. 2 a;

FIG. 3 is a sectioned representation of a sealing system of a separatorplate;

FIG. 4a is a perspective view of a sealing system of a separator plateaccording to the state of the art;

FIG. 4b is a schematic view of the sealing system of the separator platein FIG. 4 a;

FIG. 4c is a partial cross-section of the sealing system of theseparator plate in FIG. 4 b;

FIG. 5a is a perspective view of a sealing system of a separator plate;

FIG. 5b is a schematic view of the sealing system of the separator platein FIG. 5 a;

FIG. 5c is a partial cross-section of one embodiment of a sealing systemof the separator plate in FIG. 5 b;

FIG. 5d is a partial cross-section of another embodiment of a sealingsystem of the separator plate in FIG. 5 b;

FIG. 5e is a partial cross-section of another embodiment of a sealingsystem of the separator plate in FIG. 5 b;

FIG. 6a is a perspective view of a sealing system of a separator plate;

FIG. 6b is a schematic view of the sealing system of the separator platein FIG. 6 a;

FIG. 6c is a partial cross-section of one embodiment of a sealing systemof the separator plate in FIG. 6 b;

FIG. 6d is a partial cross-section of another embodiment of a sealingsystem of the separator plate in FIG. 6 b;

FIG. 6e is a partial cross-section of another embodiment of a sealingsystem of the separator plate in FIG. 6 b;

FIG. 7a is a perspective view of a sealing system of a separator plate;

FIG. 7b is a schematic view of the sealing system of the separator platein FIG. 7 a;

FIG. 7c is a partial cross-section of one embodiment of a sealing systemof the separator plate in FIG. 7 b;

FIG. 7d is a partial cross-section of another embodiment of a sealingsystem of the separator plate in FIG. 7 b;

FIG. 7e is a partial cross-section of another embodiment of a sealingsystem of the separator plate in FIG. 7 b;

FIG. 8 is a plan view of a detail of a sealing system of a furtherseparator plate according to the invention;

FIG. 9a is an oblique view of a detail of yet another embodiment of asealing system with feed-throughs through the sealing system;

FIG. 9b is a plan view of the sealing system with feed-throughs in FIG.9 a;

FIG. 10a is a plan view of a detail of a sealing system of a furtherseparator plate according to the invention with delimination elementswhich are adjacent to the sealing system;

FIG. 10b is a plan view of another embodiment of a detail of a sealingsystem of a further separator plate according to the invention withdelimination elements which are adjacent to the sealing system;

FIG. 10c is a plan view of another embodiment of a detail of a sealingsystem of a further separator plate according to the invention withdelimination elements which are adjacent to the sealing system;

FIG. 11a is an oblique view of a detail of a sealing system of a furtherseparator plate according to the invention;

FIG. 11 b is a plan view of the sealing system of the separator plate ofFIG. 11 a;

FIG. 12 is a plan view of a detail of a sealing system of a furtherseparator plate according to the invention.

DETAILED DESCRIPTION

FIG. 1 represents an electrochemical system 1 with a multitude of cells30 46 and separator plates 2 which are stacked in an alternating manner,as well as two end plates 11, 11′ which delimit the stack. The end platefacing the viewer comprises six branches 12 to 17, which serve for thefeed and discharge of reaction media and coolant: 12 indicates the feedbranch for air, 17 the discharge branch for oxygen-depleted air, 13 thefeed branch for hydrogen, 16 the discharge branch for hydrogen which hasnot been consumed, 15 the feed branch for coolant and 14 the dischargebranch for heated coolant. One can thus differentiate between six mediaflows: A indicates oxygen-rich which is to say fresh air; Doxygen-depleted air, B hydrogen, C non-consumed hydrogen, E cool coolantand F heated coolant.

FIG. 2-a shows a cell 46 of an electrochemical system 1, here a fuelcell system 1 together with the two separator plates 2 and 2′ whichdelimit the cell 46. The view is essentially in the z-direction of thecoordinate system given in FIG. 1. The electrochemical system 1 of FIG.2-a differs from that of FIG. 1 to the extent that the reduction agent,specifically the hydrogen, is not led through the stack via a portperpendicular to the plate plane, but via the two ports 23, 23′ locatedin the upper corners. Conducting the non-consumed hydrogen gas 15 onwardin the stack direction is effected via the two ports 26, 26′ located inthe lower corners. The two lateral ports 24, 25 serve for the leading ofcoolant through the stack perpendicularly to the plane of the plate. Theupper port 27 serves for leading oxygen-rich air through the stack, andthe lower port 22 for leading oxygen-deficient poor air through thestack. The layer 2 a of the separator plate 2 which lies at the topcomprises a sealing structure consisting of several beads. A bead 32which is peripheral around the electrochemically active region 29 andwhich in sections is peripheral along the outer edge 19 serves forsealing the electrochemically active region 29 or of the compartmentenclosing this region, as well as the plate as a whole, to the outside.Moreover, each of the 25 ports 22 to 27 comprises a separate bead 31,31′ surrounding the respective port.

It is to be emphasised that the ports 23, 23, 23′, 26, 26′ and 27 forthe reaction media together with the beads 31 surrounding them liewithin the region which is surrounded by the bead 32. The surface of theseparator plate 2 which faces the viewer moreover comprises a channelstructure 28, here for the distribution or air, and simultaneously formsthe electrochemically active surface 29. The bead 32 thus surrounds theelectrochemically active surface 29 in a peripheral and distancedmanner, wherein the distance changes in the course. The feed of air fromthe port 27 to the channel structure 28 and the discharge of depletedair from the channel structure 28 to the port 22 is explained in moredetail by way of FIG. 2-c.

FIG. 2-b represents a section through two separator plates 2,2′, anelectrochemical cell 46 arranged between the two separator plates 2,2′,specifically a fuel cell, as well as elements of the nextelectrochemical cell arranged on the other side of the separator plate2′. The section with respect to the represented elements corresponds tothe section B-B of FIG. 2-a, but the distances of the different elementshave been adapted with regard to a space-saving representation. Thevisible surface thus lies in a y-z plane of FIG. 1. It is clear from thesectioned representation that the electrochemical cell 46 carries acatalytic layer 42, 42′ on the actual polymer electrolyte membrane (PEM)in each case at both sides, and this layer becomes the electrode andrepresented in a distanced manner here for a better understanding. Theseelements together represent the so-called membrane electrode unit (MEA).A gas diffusion layer (GDL) 44, 44′ which consists in each case forexample of an electrically conductive non-woven of graphite lines, isarranged in each case of both sides of the MEA.

Channel structures 28 are formed into the two layers 2 a, 2 b of theseparator plate 2, and on both sides of the layer are used fordistributing media. The channel structures 28 herein form theelectrochemically active region 29. A first medium M1, specifically airis distributed on the upper side of the layer 2 a. Coolant K isdistributed on the lower side of this layer 2 a, i.e. in the cavitybetween the two layers 2 a and 2 b. A second medium M2 is distributed onthe lower side of the layer 2 b. The second medium M2 is hydrogen in thecase of a bipolar construction of the electrochemical system. In thiscase, M3 is again air and M4 is again hydrogen. With a monopolarconstruction of the electrochemical system, the second medium M2 isagain air. In contrast, with a monopolar construction, the channels onboth outer surfaces of the second separator plate 2′ serve for thedistribution of hydrogen which here represents the third and fourthmedium M3 and M4. In the case of a bipolar construction, all separatorplates of a stack are identical, and in the case of a monopolarconstruction, as the case may be two different separator plate variantsalternate along the stack.

It is also clear from the section of FIG. 2-b that the bead 31 surroundsthe through-opening 23 and thus seals off the hydrogen port. The bead 31which peripherally seals off the electrochemically active region, in therepresented section in contrast runs essentially along the outer edge 19of the layer 2 a of the separator plate 2, so that it is only sectionedonce in the section shown here. It is also evident from the sectionedrepresentation that the height of the beads 31, 32 amongst one anotheris essentially identical, wherein the height of the beads 31, 32 howeveris significantly higher than the height of the channel structures 28.

FIG. 2-c represents the layer 2 a of the separator plates 2 which liesclosest to the viewer in FIG. 2-a, in a plan view, thus againcorresponds to a view in the z-direction of FIG. 1. Here, the design ofthe beads 31, 31′ and 32 is to be dealt with in more detail. The bead31′ peripherally surrounds the port opening 25 and herein, disregardingthe waved structure of the bead itself, has a small, essentiallyconstant distance to the edge of the port opening 25. The bead 31surrounds the port opening 26′ in a comparable manner, but as a rule hasan essentially circular course without a wave structure. Here too, thedistance to the edge of the port is essentially constant. The bead 32runs along and distanced to the outer edge 19 of the layer 2 a of theseparator plate 2 and herein not only encloses the electrochemicallyactive region 20 which it seals off, but also the ports 22,23,23′,26,26′and 27, together with the beads 31 sealing them. In the representedexample, the bead 32 comprises several sections 35, in which the beadroof has a wave-like course. These sections 35 considered per se,macroscopically have a straight-lined course. It is evident that thesections 35, in which the bead 32 has a wave-like course of the beadroof, are arranged in each case in elongate, straight-lined sections ofthe sealing system, whereas relatively greatly curved regions of thebead 32, such as the region S surrounded by an oval, have a shape of thebead roof which corresponds to the total extension direction of the bead32 in respective section, thus has no periodic wave-like course.

It can also be recognised from FIG. 2-c that air flows out of the port27 along the continuations 33 through the bead 31, in order to hence getto the electrochemically active region 29 where the oxygen contained inits reacts with protons which enter through the MEA. The air which isdepleted of oxygen in such a manner and has a high moisture content as aresult of the reaction, then flows further downwards to thecontinuations 33 and there passes the bead 31 anew and is led via theport 22 to the end plate. The continuations are herein formed into theflanks of the bead 31 such that the sealing is not compromised.

FIG. 3 basically represents the size ratios and angular details in asealing system of a separator plate, as are applied hereinafter. Thesection of FIG. 3 herein corresponds for example to the section C-C inFIG. 2c , thus lies in a plane parallel to the y-z plane of FIG. 1. Thetotal width of a bead 3 of a sealing system is indicated at W_(T), andthe width of the bead roof 39 is indicated at 15 W_(D). The inner andthe outer base width W_(I) and W_(A) respectively are identical in theconsidered symmetrical bead cross section, so that for simplification,the term W is used instead of the different terms W_(I), W_(A). Thissimilarly applies to the inner and outer flank angle α_(I) and α_(A),which are analogously indicated in a simplified manner by α. The heightof a bead in an individual layer 2 a, 2 b of a separator plate 2 isindicated at H. FIG. 3 furthermore illustrates the different sections ofa cross section of a bead 3 from the right to the left: subsequent to afirst bead foot 37 is a bead flank 38, and the bead roof 39 connectsafter a further bend point. On the other side of the bead roof, afurther bead flank 38′ is subsequent to a further bend, and after thiscomes the second bead foot 37′. The bead feet are 25 defined as theboundary points which are adjacent to a bead flank at their side whichis away from the bead roof and on which the tangent to the course of thelayer runs parallel to the middle plane of the separator plate 2. If abead is considered independently of its function as a sealing element 32around an electrochemically active region 29 or as a sealing element 31,31′ of an inner 30 edge, then here and hereinafter it is indicated at 3.

FIG. 3 further illustrates as to how the two layers 2 a, 2 b of aseparator plate 2 are designed in an essentially mirror-symmetric mannerand are in surfaced (extensive) contact with one another in the regionoutside the bead 3, more precisely beginning at the bead feet 37, 37′.The representation of the channel structure has been done away with, andhere the explanations in the context of FIG. 2-b are referred to.

The embodiments concerning FIGS. 1 to 3 apply to the separator plates ofthe state of the art as well as to the separator plates according to theinvention.

The wave-like course of a section of a bead 3 of the state of the art,with which the bead roof 39 extends with a constant width W_(D),specifically 1.6 mm, in a wave-like manner with at least two waveperiods with a wavelength λ, is show in FIG. 4 in three part-pictures,by way of a detail of an individual layer 2 a of a 15 separator plate 2.The sectioned representation of FIG. 4-c herein corresponds equally toall three section lines AD-AD, BD-BD and CD-CD which are given in FIG.4-b. The two bead flanks 38,38′ have a constant base width W of 0.7 mmin each case, over the entire course. The total width of the bead 3W_(T) is thus 3 mm. Because the base width of the bead flanks 38, 38′does not change over the course of the bead, and the base width of thebead flanks 38, 38′ at both sides of the bead roof 39 is likewiseidentical, the bead consequently has a uniform flank angle α. Adifferentiation of the flank angle into the outer angle which is to saythe flank angle in the convex section, α_(A), and the inner angle whichis to say the flank angle in the concave section, α_(I), is thus notpossible with the separator plate 2 of the state of the art. The anglesα are 35° in each case. FIG. 4-b moreover underlines the fact that theamplitudes of the respective bead feet and of the two transition curvesbetween the bead roof and the bead flanks adjacent thereto areidentical.

FIG. 4-b further illustrates the convex and concave regions which extendin each case between two dashed lines, which is to say the section linesCD-CD which in each case represent a perpendicular to the tangent to theneutral lines of the bead roof 39. Apart from these, the upper and thelower inner radii r_(IO) and r_(IU) and the upper and lower outer radiir_(AO) and r_(AU) are also derived from virtual circles which areindicated by double-dot dashed lines. Whereas an above-average stiffnessof the beads is given in the concave regions, in which thus inner radiiare present, this is below average in the convex regions, in which outerradii are present. This is a consequence of the inner support in theconcave regions due to the bead sections facing one another. The regionsof a low bead stiffness are indicated at g, the regions of a high beadstiffness are indicated at h. Leakages can occur due to thisnon-uniformly distributed bead stiffness, since media can flow throughthe sections of a low bead stiffness and penetrate into regions, inwhich these media should not enter. The present invention provides aremedy for this.

Comparable representations of a bead 3 as represented in FIG. 4 aregiven in FIG. 5, but here now for a first embodiment of a separatorplate 2 according to the invention. Whereas in the preceding example ofthe state of the art, the cross sections perpendicular to the tangent tothe neutral lines of the bead roof 39 are identical at all points of thewave-like course of the bead roof 39, here they significantly differfrom one another. For this reason, FIG. 5 comprises threecross-sectional representations, wherein FIG. 5-c represents the crosssection at inflection points, i.e. the sections AE-AE and DE-DE of FIG.5-b. FIG. 5-c thus corresponds to FIG. 4-c. FIG. 5-d represents thecross section BE-BE at the wave peak and FIG. 5-e the cross sectionCE-CE at the wave trough, of the bead of FIG. 5-b. The width of the beadroof 39, W_(D) remains constant over the entire wave-like course of thebead roof 39 and is 1.6 mm as in the preceding example of the state ofthe art. The inflection points, which delimit the convex sections of thebead 3 from the concave sections, as in the preceding example arerepresented by dashed lines which is to say lie on the two section linesAE-AE and DE-DE. The line T marks the main extension direction of thebead 3 and results from the connection line of the inflection points ofthe neutral lines of the bead roof. In the convex regions, whose beadflanks 38, 38′ are characterised in FIG. 5-b by a hatching in each case,the base width W_(A) of the respective bead flanks 38, 38 is reducedsuch that beginning at the inflection point, it reduces up to the apexpoint and increases again from the apex point up to the next inflectionpoint. The base width at the inflection points is 0.85 mm, and at theapex point in contrast is only 0.65 mm. In the concave regions, thewidth W_(I) of the respective bead flank 38, 38′ in contrast runs in aconstant manner with a base width of 0.85 mm. The total width of thebead W_(T) thus alternates between 3.1 and 3.3 mm. The amplitude of thebead feet here is somewhat larger than the amplitude of the transitionlines between the bead roof and bead flanks, and the ratio is roughly1.25:1.

The flank angle of the concave region a1 accordingly remains constantover the respective concave region, and it is 35°, as the angle α at theinflection points. In contrast, the flank angle α_(A) of the convexregion, beginning at the inflection point, increases from 35° to 60° atthe apex point and then reduces again to the next inflection point to35°. The bead flank in the region, in which it has a low bead stiffnessin the state of the art—cf. the characterisations g in FIG. 4-b—isstiffened by way of the steeper flank angle, so that as a whole, thebead has a constant stiffness over its wave-like course.

Here, it is to be noted that the references W_(A) and α_(A) each relateto the convex sections, and the references W₁ and α₁ each relate to theconcave sections and thus jump from one bead flank to the opposite oneat each inflection point.

FIG. 6 again with five part-pictures represents a second embodiment of aseparator plate 2 according to the invention, by way of details of itsbead 3. Again the cross section at the inflection points, which isrepresented in FIG. 6-c, corresponds essentially to the cross section ofFIG. 4-c, since the bead 3 here seems to be formed symmetrically.However, FIG. 6-b illustrates the fact that the bead flanks 38, 38′ inthe concave regions between the inflection points are each widened, sothat here too, a bead 3 as a whole has an asymmetrical course.

The bead 3 of the embodiment according to FIG. 6 basically differs fromthe bead 3 of the embodiment according to FIG. 5 in that the bead roof39 is designed somewhat more narrowly, specifically only has a widthW_(D) of 1.2 mm.

The base width of the bead flanks W is 0.6 mm at the turning points. Theouter flank W_(A) of the bead extends with this base width frominflection point to inflection point. In contrast, the base width of theinner flank W_(I), beginning at an inflection point, enlarges from 0.6mm to 0.8 mm at the wave trough, so as to reduce again to 0.6 mm in itscourse up to the next inflection point. The total width W_(T) of thebead 3 in this embodiment varies between 2.4 and 2.6 mm.

Accordingly, the flank angle of the outer flank α_(A) remains constant,and here it is 34°. In contrast, the flank angle of the inner flankα_(I) decreases over the course of the concave section from inflectionpoint to inflection point, from 34° to 26° at the wave trough, so as toincrease again to 34°. On account of this, the bead stiffness reduces inthe regions which in FIG. 4-b are characterised by h due to theirabove-average bead stiffness, and the bead stiffness is thus homogenisedat both bead flanks 38, 38′ over the wave-like course of the bead 3, sothat leakages are prevented. The regions, in which the base width of abead flank 38, 38′ changes, are characterised by hatching in FIG. 6-b.

Rounding up, it should be emphasised that the amplitudes of the beadfeet are roughly only ⅔ of the amplitude of the transition lines betweenthe bead roof 39 and the bead flanks 38, 38′.

FIG. 7 represents an embodiment of the invention, with which the basewidth of the bead flank W_(A) decreases and increases again over theconvex sections and the base width of the bead flank W_(I) increases andreduces again over the concave sections. A hatching of the regions, inwhich the base width changes, has therefore been done away with. As withboth preceding embodiment examples, T marks the main extension directionof the bead in the represented detail. The flank angle α_(A) over aconvex section thus undergoes an increase up to the apex point and adecrease follows this, and in a concave section the flank angle α_(I) incontrast undergoes a decrease, subsequent to which an increase followsafter the apex point. The embodiment example according to FIG. 7 thusunifies both approaches which have been applied separately from oneanother in the embodiment examples of FIGS. 5 and 6, for homogenisingthe bead thickness over the wave-like course of the bead roof, by whichmeans a particularly effective and thus advantageous homogenisation ofthe bead thickness is obtained.

Specifically, the width of the bead roof W_(D) is 1.2 mm, whereas thebead flanks at the apex point which is further from the main extensionline T have a minimum of their width W_(A) of 0.6 mm, which is followedby an increase up to the next inflection point to a width W of 1 mm andfurther up to the apex point lying closer to the main extension line Tto a maximum of the width W_(I) of 1.4 mm. The flank angles α at theinflection points are 21°, and the flank angles α are thereforeshallower than in the preceding embodiment examples. The flank angleα_(A) increases to 42° towards the apex point remote from to the mainextension line T, and the flank angle α_(I) decreases to 16° towards theapex point lying closer to the main extension line T.

It is particularly noticeable that the total width WT of the bead 3remains constant over the complete section, in which the bead roof 39runs in a wave-like manner, by which means the spatial requirement ofthe embodiment according to FIG. 7 is particularly low, so that thisembodiment is particularly advantageous. The total width W_(T) of thebead 3 is 3.2 mm here.

FIG. 8 illustrates a further embodiment of a separator plate 2 accordingto the invention, now on its own and by way of a plan view of a sectionof the bead 3, whose bead roof runs in a wave-like manner in therepresented section.

As in the embodiment example of FIG. 7, the flank angle of the convexsections is enlarged, as well as the flank angle of the concave sectionsreduced. Accordingly, the base widths at the apex points, thus at thewave peaks and troughs, are enlarged compared to the base widths of theinflection points. As with the embodiment example of FIG. 7, the totalwidth W_(T) of the bead 3 runs in a constant manner in the representedsection with a wave-like course of the bead roof 39. Whereas the beadfeet run in a straight line in the embodiment example of FIG. 7, herethe bead feet run with a significantly reduced amplitude, which isroughly 0.45 times the amplitude of the delimitation lines of the beadroof.

FIG. 9 represents a section of a bead 3 of a separator plate 2 accordingto the invention, said bead comprising continuations 33 on both beadflanks 38, 38′, as has already been explained in the context of FIG. 2.Here, it is clear that the continuations on both bead flanks 38, 38′ areperiodically arranged at a distance λ/2, and specifically in each casein the region of the inflection points of the wave-like course of thebead roof 39. The continuations 33 serve for leading a medium throughthe sealing barrier of the bead 3, and this being at that surface of thelayer 2 a of the separator plate 2 which is way from the viewer,specifically between the two layers 2 a and 2 b. It is evident from FIG.9 that the continuations each consist of two feet which in FIG. 9-bextend vertically, and of two flanks as well as a roof, wherein the feetof the continuations, although lying in the same plane as the bead feet,the total height of the continuations however is smaller than the heightof the bead 3, so that the continuations only marginally influence thepressing behaviour of the bead. The bead feet 37, 37′ are interrupted inthe region of the continuations. The continuations 33 are only formed inthe layer 2 a lying at the top. The bead of this embodiment correspondsto that of the embodiment according to FIG. 5 with regard to itsremaining design, in particular with regard to the wave-like course ofthe bead roof 39 and the reduction of the base width W_(A) and theincrease of the flank angle α_(A) in the convex regions relative to theadjacent inflection points.

FIG. 10a shows a section of a bead 3 of a separator plate 2 according tothe invention, said separator plate having two continuations 33distanced to one another by a wavelength k, only on the bead flank 38which lies at the bottom in the figure. The continuations here serve asa barrier between the channel structure which is not represented andwhich connects below the represented detail, and the sealing structure.They prevent medium outside the electrochemically active region fromflowing past the gas diffusion layers 44 and 30 44′ shown in FIG. 2-band thus not being available to the electrochemically active electrodes42, and 42′. This would lead to unacceptable loses on utilisation of thecombustion gases and thus to a significant reduction in the efficiencyof the electrochemical cell

FIG. 10b shows a section of a bead 3 of a separator plate according tothe invention. This is an embodiment, in which only one bead flank 38(with bead foot 37) changes, whereas the flank 38′ which in this caselies opposite the continuations remains constant and thus the bead foot37′ runs parallel to the bead root 39. The increase of the flank anglein concave regions and represented in FIG. 10b is only one possibility.In a further embodiment (represented in FIG. 10c ) the flank angleincreases from the infection points (α and α_(A)=21°) to the apex pointin the concave regions (α₁=32°). The advantage of the respectiveembodiment results from a targeted possibility of adapting the beadcharacteristics to the geometric changes by way of incorporating thecontinuations 33 into the bead flanks 38

The described, single-side changes of the flank angle is not onlylimited to the regions, in which the continuations 33 are incorporatedinto a bead flank, but can analogously be applied n any other region ofthe wave-like bead region on a separator plate 2, 2′. Here, either thebead flank which faces the active region or the outwardly directed beadflank can be adapted and this can also be varied individually in thedifferent regions of the separator plate, according to the local demandson the bead characteristics.

A further embodiment of a separator plate 2 according to the inventionis shown in FIG. 11 by way of an oblique view and a plan view, whereinhere, both layers 2 a, 2 b of the separator plate 2 are represented, incontrast to the previous oblique views with the exception of FIG. 9-a.Here, the bead flanks run with a constant base width, and here weldconnections 60, 60′ which essentially with their radius runconcentrically to that of the bead feet 37, 37′ of the two layers 2 a, 2b of a separator plate 2 are sectionally provided in the convex regions,for homogenising the bead pressing. The extension of the weldconnections 60, 60′ here corresponds precisely to the extension of theconvex region, i.e. from a perpendicular to the tangent to the neutrallines of the bead roof 39 through a first inflection point up to the aperpendicular up to the tangent to the neutral lines of the bead roof 39through a second inflection point adjacent to the first inflectionpoint. The weld connections are herein provided in all shown convexregions, so that weld connections are given on both sides of the bead.

FIG. 12 shows a variant of the embodiment of FIG. 11, with whichembodiment it is merely the extension of the weld seams which isreduced, compared to the embodiment of FIG. 11. Here it is roughly 20%of the wavelength λ.

1-17. (canceled)
 18. A separator plate for an electrochemical system,comprising: two metallic individual plates, wherein the metallicindividual plates comprise through-openings at least for operatingmedia, as well as distribution structures which are formed into theindividual metallic plates and which each communicate with at least twoof the through-openings, wherein a peripheral sealing structure isformed into each of the metallic individual plates at least peripherallyaround at least one of (1) the electrochemically active region anddistanced from this and (2) peripherally around at least one of thethrough-openings and distanced from the edge of these through openings,the cross section of said sealing structure comprising a bead roof, twobead flanks and, at least in sections, two bead feet, wherein thesealing structure at least in the region of its bead roof extends, atleast in sections, in a wave-like manner with at least two wave periodswith convex and concave sections, so that upper inner and outer radiiform at the transition from bead roof to the bead flanks and lower innerand outer radii form at the bead feet, weld connections are sectionallyprovided between the two metallic individual plates of the separatorplate, at least at one side adjacent to the bead feet at least along theregion in which the bead roof extends in a wave-like manner, wherein ineach case the weld connections extend in the region adjacent to a convexregion of the wave course and concentrically to the bead foot of theconvex region.
 19. The separator plate according to claim 18, whereinthe weld connections each extend over at least 1/9 of the wavelength λ,and maximally over the complete convex section.
 20. The separator plateaccording to claim 18, wherein the sealing structure comprises a coatingat least in the region of the bead roof.
 21. The separator plateaccording to claim 20, wherein the coating comprises FPM (fluorocarbonrubber), silicone rubber or NBR rubber (acrylonitrile butadiene), PUR(polyurethane), NR (natural rubber), FFKM (perfluoroelastomericcompounds), SBR (styrene butadiene rubber), BR (butyl rubber), FVSQ(fluorosilicone), CSM (chlorosulphonated polyethylene), silicon resin,epoxy resin or mixtures of the above-mentioned substances or contactadhesive or a physically setting adhesive.